Once the aching in Rebecca Adlington's limbs subsides, and that will take some time, another, deeper pain will hit her. She has said that before her races here in London she felt so nervous she went "from feeling sick to feeling faint to feeling angry to feeling like I want to cry". After she came third in the 800m final there was an equally confusing cocktail of emotions going on in her mind.

Adlington was proud at what she had achieved and so she should be. She has competed in four Olympic finals and won a medal in each one of them. But she was distraught with her performance, breaking into tears on the podium. And she was overwhelmed by the crowd, who chanted her name in celebration and appreciation as she left the Aquatics Centre for the last time.

Who knows which of those feelings will be the one that lingers longest in her memory and which will subside with time? Certainly the simple, unavoidable, truth is that both she and the British public had been hoping for so much more from this race. The 800m is her favourite event and Adlington is the world champion at it. She had swum the two quickest times in the world this year, until Friday night, when 15-year-old Katie Ledecky, the youngest member of the USA's Olympic team, swam the second-fastest 800m in history. The only woman who has ever gone faster is Adlington herself, in the final in Beijing.

The 23-year-old did not want to offer excuses but her explanation sounded a little like one. "The pressure and the expectation coming into these Games has all been a little bit of a battle," she said. Like so many other British swimmers, she seemed to be pulled down by the burden of the occasion, rather than lifted up by all the support she has had. Before the Olympics started Britain's head coach, Dennis Pursley, said that he wanted to make his team "look forward to the advantages of a home Olympics, rather than fear the pressures". He tried and he failed.

So much was resting on Adlington's swim. The British team were depending on her to deliver. "I am so proud and pleased to get a bronze medal – it's nothing ever to be embarrassed about," she said. "Swimming is one of the hardest sports to medal at. It is so, so difficult and I hope the public realise that." She is right, and the public can and will celebrate what she has done. But look just a little harder and you will find that Adlington, as she said herself, has "swum faster than this all year". She was 1.5sec quicker when she won the Olympic trials in March.

"I would have liked the time to have been a bit quicker, I'm not going to lie," Adlington said. "I've done that time all year and I don't know what happened. Everything kind of caught up with me."

Adlington was not just beaten by Ledecky, she was blown away by her. The American led from start to finish, opening up a lead in the first 100m that Adlington, like everyone else here, kept expecting to shrink. It never did. Ledecky won in 8min 14.53sec. Swimming is becoming a young woman's game – Ledecky is the second 15-year-old to win a gold medal at these Games, after Lithuania's Ruta Meilutyte. Ye Shiwen, who has won two golds, is 16. And Missy Franklin, who has won three, is only a year older. Ledecky, like Ye, knocked more than five seconds off her personal best. Chinese fans will wonder whether she will be subject to the same insinuations and accusations.

It was not meant to be like this. The race was supposed to be all about Adlington's battle with her old rival Lotte Friis. The two of them have fought for every major title since 2008. It is possible they were so preoccupied with each other that they forgot about everyone else. Certainly no one reckoned Ledecky was a real contender until it was too late. She took the race out hard and fast. By 200m she was almost 1.5sec inside the world record time. Adlington and Friis, flustered, did not know how to respond. Should they let the kid blow herself out? Or should they reel her back in? In the heat of the race, they chose to wait and see. They were guided by Ledecky's performance in the heats, when she had made a similar start before fading badly as the race went on.

So Adlington and Friis, the two great female long-distance freestylers of their era, sat back. And Ledecky just kept on going. At halfway she was a body length up on Adlington, who was holding on to second place. By now people were starting to panic, not least Adlington herself. Sensing that the situation demanded it, she tried to make a move but she could not summon up the change of pace she needed. By 700m Adlington had blown it. She could not catch up and, worse still, Spain's Mireia Belmonte García was starting to move up in lane six.

Belmonte García was another unknown contender. She is a freestyle and butterfly swimmer and had never competed in the 800m freestyle at a major championships before. But she cruised past Adlington, who then found herself trying to hang on to bronze. Friis fared even worse. Broken by Ledecky, she slipped back to fifth.

So in the end Adlington did well to win a medal at all. She has produced two brave performances in her finals at these Olympics, each of them a testament to her grit and determination. But after London the golden days of Beijing are now just a distant memory.